MCAT Question, please help.

[thestrugglingturtle]

Suppose an individual lacked an enzyme necessary for proper functioning of Complex II and, as a result, significant energy was lost during electron transfer to this portion of the electron transport chain. Which of the following describes the mostly likely pattern of ATP production from mitochondrial electron carriers in this individual?

A. Mitochondrial NADH generates 1 ATP per molecule, while mitochondrial FADH2 generates 1.5 ATP per molecule.

B. Mitochondrial NADH generates 2.5 ATP per molecule, while mitochondrial FADH2 generates 0.5 ATP per molecule.

C. Mitochondrial NADH generates 1 ATP per molecule, while mitochondrial FADH2 generates 0.5 ATP per molecule.

D. Mitochondrial NADH generates 2.5 ATP per molecule while mitochondrial FADH2 generates 1.5 ATP per molecule.

THANK YOU SO MUCH

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[Professional Student]

In the normally functioning ETC, electrons from NADH enter at complex I where 4 protons are pumped out. Electrons from FADH2 enter at complex II where no electrons are pumped out. Electrons from both sources are transported by CoQ to complex III, meaning the electrons are of equivalent energy potential after the complex where they enter. NADH typically results in 2.5 ATP produced per molecule, while FADH2 results in 1.5 ATP produced per molecule. Since improper functioning of complex II only affects electrons from FADH2 your correct answer is B.

I recommend reviewing the ETC to the point were you can identify the pathways of each electron, even the steps within each complex.

 

[thestrugglingturtle]

In the normally functioning ETC, electrons from NADH enter at complex I where 4 protons are pumped out. Electrons from FADH2 enter at complex II where no electrons are pumped out. Electrons from both sources are transported by CoQ to complex III, meaning the electrons are of equivalent energy potential after the complex where they enter. NADH typically results in 2.5 ATP produced per molecule, while FADH2 results in 1.5 ATP produced per molecule. Since improper functioning of complex II only affects electrons from FADH2 your correct answer is B.

I recommend reviewing the ETC to the point were you can identify the pathways of each electron, even the steps within each complex.

Thank you so much, so helpful

 

[abz]

But why does the amount of ATP decrease for FADH2 if complex II does not participate in pumping out electrons?

 

[3AA]

But why does the amount of ATP decrease for FADH2 if complex II does not participate in pumping out electrons?

I think it's because even though Complex II does not pump out H+, as was mentioned previously, e- from complexes I and II are sent to complex III, which does pump out H+ --> less e- sent to complex III = less H+ proportionally pumped = less ATP made

Can someone verify this?